iterating "by twos"

[kj]

Is there a special pythonic idiom for iterating over a list (or
tuple) two elements at a time?

I mean, other than

for i in range(0, len(a), 2):
    frobnicate(a[i], a[i+1])

?

I think I once saw something like

for (x, y) in forgotten_expression_using(a):
    frobnicate(x, y)

Or maybe I just dreamt it!  :)

Thanks!
-- 
NOTE: In my address everything before the first period is backwards;
and the last period, and everything after it, should be discarded.